It is known in the prior art that golden colored articles may be manufactured by depositing titanium in a nitrogen-containing atmosphere to form a layer of titanium nitride on a thermally resistant substrate. By controlling the amount of nitrogen available to react with the titanium, the color of the titanium nitride coating can be made to be similar to that of pure gold or of yellow gold alloys. However, due to the interaction of visible light at its surface, titanium nitride is much less brilliant than the gold or yellow alloys that it simulates. This well-known property of titanium nitride can be circumvented by the expedient of applying an additional coating of gold or a yellow gold alloy over the titanium nitride coating. U.S. Pat. No. 4,252,862 describes such a process. In this way, titanium nitride films have been used to increase the apparent wear life of decorative gold or gold alloy final coatings where they are substituted for or used atop the nickel underlayers whose use is well known in the electroplating art. Under conditions of continuous service in the hands of users, the relatively soft gold-containing layer scratches and develops a diffusely reflecting appearance and is simultaneously worn away, especially from exposed and prominent features of the coated substrate. When the gold-containing layer wears completely away from such prominences and the darker titanium nitride underlayer is exposed, the visual contrast thus produced is not as great as in the case where a nickel underlayer is exposed. But the fact that the gold-containing layer has worn away is not completely concealed since there still exists a visual contrast between the remaining brilliant and diffusely reflecting, scratched gold-containing regions that surround the darker and specular, scratch and wear resistant titanium nitride underlayer.
The films of the present invention avoid the inferior wear properties of gold or yellow gold alloys and the inferior appearance of titanium nitride. As a consequence of their structure, the films of the present invention integrate the superior appearance of gold or yellow gold alloys with the superior wear resistance of titanium nitride. When subjected to wear, the microlaminated films of the present invention retain their billiant and specular appearance and do not develop visually contrasting areas.
It is also known to simultaneously deposit titanium and gold or gold alloys in the presence of nitrogen. The codeposition approach produces films in which the constituent elements are mixed on an atomic scale and whose properties are uniform throughout their thicknesses. However, this atomic-scale mixing of elements does not result in the simple integration of the desirable properties of titanium nitride and gold. Rather, when gold or a gold alloy is codeposited with titanium in the presence of nitrogen in accordance with the prior art processes, films are produced whose properties are deficient in certain key areas: the mixed films possess a color which is substantially less yellow than either titanium nitride or the original gold or gold alloy; and the mixed films are less resistant to corrosion than either titanium nitride or the original gold or gold alloy As explained more fully hereinafter, these undesirable properties result from the presence of substantial amounts of gold-titanium intermetallic compounds which form during the growth of the codeposited films. In addition, these mixed films are less brilliant than the gold or gold alloy which is used to form them. It is also known to produce films in which there exists a continuous or stepwise gradient of composition from an underlayment of primarily titanium nitride to primarily gold or gold alloy at the free surface of the film. Films of this type necessarily have transition regions where, as a result of the atomic-scale mixing which promotes the interaction of gold and titanium, the desirable properties of the separate substances are degraded, as described hereinbefore.
For coated components which are subjected to conditions of wear and abrasion, all film regions are ultimately exposed as a free surface. The processes of wear decrease the quality of film structures which begin their service life with regions of inferior properties within the film.
It is a feature of the present invention that the formation of substantial quantities of gold-titanium intermetallic compounds is avoided and that the quality of components coated with these microlaminated but unmixed films is uniformly superior throughout their service life.